Adsorption and Permeation of Porphyrins through Lipid Membrane

Abstract

Photosensitizers (PS) are key compounds of photodynamic therapy killing tumor cells by singlet oxygen generated under illumination. Their efficiency relies on their capability of damaging molecules important for the cellular metabolism. Penetration of PS through the membrane may enhance such efficiency. This investigation is oriented to study the permeability in lipid membranes (BLM) of different PS, which are porphyrin structures, including anions 5,10,15,20-tetrakis(p-sulfonatophenyl)porphyrin (H2TPPS4), β-imidazolyl substituted porphyrin including Zn(II) and In(III) complexes; and phosphorus (V) complexes of meso-(p-pyridyl)-triphenylporphyrin bearing hydroxyl and ethoxyl axial ligands. The permeability of these compounds was studied by a method based on measurements of the difference of boundary potentials (DBP) and its dependence on pH of the solutions on two sides on BLM previously developed by authors (Bioelectrochem.and Bioenerget. 23, 17-26). We found that anions H2TPPS4 and β-imidazolyl substituted porphyrins do not penetrate the BLM, and the dependence of DBP on pH is caused by their pH-dependent aggregation. In contrast, some of phosphorus porphyrins can penetrate through BLM, which is observed by an increasing of DBP with decreasing of pH on both sides of BLM. The value and sign of DBP depend on the difference of pH on two sides of the membrane, DpH. The most significant effect of DpH was observed on the phosphorus (V) complexes - meso-(p-pyridyl)-triphenylporphyrin containing one pyridine peripheral group. The effects of pH disappeared on the phosphorus (V) porphyrin with two pyridine groups. In conclusion, the efficiency of the PS permeation depends on the structure of the molecule. The study is supported by Russian Scientific Fund No 19-13-00410 and RFBR No 19-04-00694.